<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
</html>
<script>
    function conver(limit){
        var size = "";
        if( limit < 0.1 * 1024 ){ //如果小于0.1KB转化成B
            size = limit.toFixed(2) + "B";
        }else if(limit < 0.1 * 1024 * 1024 ){//如果小于0.1MB转化成KB
            size = (limit / 1024).toFixed(2) + "KB";
        }else if(limit < 0.1 * 1024 * 1024 * 1024){ //如果小于0.1GB转化成MB
            size = (limit / (1024 * 1024)).toFixed(2) + "MB";
        }else{ //其他转化成GB
            size = (limit / (1024 * 1024 * 1024)).toFixed(2) + "GB";
        }

        var sizestr = size + "";
        var len = sizestr.indexOf("\.");
        var dec = sizestr.substr(len + 1, 2);
        if(dec == "00"){//当小数点后为00时 去掉小数部分
            return sizestr.substring(0,len) + sizestr.substr(len + 3,2);
        }
        return sizestr;
    }

    console.log(conver(21316803792))
</script>
